1. Field of the Invention
The present invention relates generally to the direct attachment of semiconductor chips to a substrate or module with the use of a thermoplastic interposer therebetween. More particularly, the subject invention pertains to the direct attachment of semiconductor chips to a substrate or module with a thermoplastic polymer interposer and a joining material preferably formed of a composite of a thermoplastic polymer such as a copolymer of polyimide and siloxane and a fine metal such as gold powder.
2. Discussion of the Prior Art
Direct chip attachment of semiconductor chips to multichip modules has been practiced commercially, and offers obvious advantages in terms of density and performance. Although there are advantages to direct chip attachment on multilayer ceramic (MLC) modules, there are also disadvantages associated therewith. High temperature solder is normally used for reliability related reasons for the electrical connections, with the joining temperature cycling up to 370.degree. C., which limits the choice of materials which can be used in the components, particularly with respect to polymers.
Burn-in and testing of multichip modules is performed on a module populated with many chips. This results in a great deal of rework, and subsequent solder reflows over the entire module substrate, generally for the purpose of reattaching only one or two chips. Therefore, the multichip module, including metallurgies on both chip and substrate sides thereof, is required to be designed to withstand ten to twenty reflow cycles. Accordingly, although this technology offers a number of advantages, it also has a number of disadvantages associated therewith.
The present invention incorporates some of the advantages of this existing technology which can use a controlled collapse chip connection (C-4) pattern on the chips, while alleviating several of the problems associated therewith.
Several U.S. Patents have been evaluated as prior art relative to the present invention, but all are quite distinct for the following reasons. U.S. Pat. No. 4,648,179 fabricates an interconnection layer which is bonded to a module, but does not disclose or teach chip interconnection/encapsulation. U.S. Pat. No. 4,179,802 uses metal studs that have been electroplated, and uses small amounts of solder to make the electrical connections which are essentially direct stud connections. In contrast thereto, the present invention preferably uses a metal-polymer composite to provide the electrical connections, and provides encapsulated connections joining the chip to the substrate. U.S. Pat. No. 4,642,889 uses fine wires which are positioned within a paper interposer surrounded by solder and flux, which are then heated and melted to make the electrical connections. Afterwards, the paper interposer is totally removed by dissolving it in a washing operation. In contrast thereto, the present invention uses the interposer to both join and encapsulate the chip to a substrate or module.